Pier foundation system for manufactured building structures

ABSTRACT

A foundation system for a manufactured building structure includes a pier for attaching the building structure to a foundation.

BACKGROUND

Manufactured buildings and structures such as prefabricated homes and trailers are typically fabricated at a factory, and then transported to a site for installation on a foundation. Simple piers and other foundations supports have been used to support the manufactured structures at the installation site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an exemplary prefabricated structure installed on an exemplary embodiment of a foundation support system.

FIG. 2 is a diagrammatic top view of an exemplary embodiment of a foundation support system.

FIGS. 2A-2C diagrammatically depict exemplary respective foundation systems for a single wide building structure, a double wide structure with a tag unit, and a triple wide structure.

FIG. 3 is an isometric view of an exemplary embodiment of a mounting pier of a foundation support system.

FIG. 4 is a front cross-sectional view of the mounting pier of FIG. 3.

FIGS. 5-6 illustrate an exemplary construction of a footing for a foundation system.

DETAILED DESCRIPTION

In the following detailed description and in the several figures of the drawing, like elements are identified with like reference numerals. The figures are not to scale, and relative feature sizes may be exaggerated for illustrative purposes.

An exemplary embodiment of a manufactured building structure 10 is illustrated in FIG. 1. The structure is supported above site surface 20 by a foundation system which includes a configuration of standard piers 40 and ground acceleration damper piers 50. The standard piers may be the well known pyramid-shaped pier structures. In this exemplary embodiment, the manufactured building structure 10 is a double-wide housing trailer structure. It is to be understood that the manufactured housing structure 10 may be other types of structures, including without limitation a single-wide trailer, a triple-wide trailer, or a double-wide trailer with a tag unit structure, just to name a few.

The structure 10 may have a width of ten, twelve or fourteen feet in an exemplary embodiment, for each unit. Thus, for a double-wide unit, the nominal width may be twenty feet, twenty-four feet or twenty-eight feet, in this example. The length of the structure in an exemplary embodiment may vary from thirty six feet to sixty six feet.

In this exemplary embodiment, as depicted in FIG. 2, the structure 10 includes single-wide units 10A and 10B, which are secured together along a common longitudinal wall 12. Each single-wide unit is fabricated on a chassis comprising a pair of longitudinal chassis beams 14. The chassis beams 14 may be I beams, C beams, hot rolled channel beams, or other beam constructions.

The housing structure is attached to, and supported by, the configuration of piers 40 and 50. FIG. 2 illustrates a typical arrangement of the piers relative to the set of chassis beams 14 for the structure 10. The standard piers 40 are spaced along the longitudinal extent of each of the beams, and may have a standard spacing distance specified by the manufacturer of the structure 10 or by building codes, for example. The standard piers are attached to the site surface 10, e.g. to a concrete pad or to a concrete foundation set into a ground surface. The piers are also typically attached to the chassis beams, e.g. by bolts or fasteners.

Also providing foundation support are the piers 50, each of which is attached to a chassis beam 14, and are depicted in further detail in FIGS. 3-4. The GAD piers 50 are interspersed among the standard piers along the lengths of the chassis rails. In an exemplary embodiment, a GAD pier 50 is located near each corner of the structure 10 along each of the outside rails 14 with an intermediate pier 50 between the corner piers. Two piers are spaced along each interior rail 14. Other dispersal arrangements may alternatively be employed for the GAD piers. The number, spacing and locations of the GAD piers 50 and standard piers 40 for a given application may be determined by engineering calculations according to such parameters including the building structure size parameters, the type of standard piers used, and the site details. For example, if the standard piers are conventional pedestals which are unsecured to the rails 14 or to the site surface, more GAD piers may be used than in a particular application in which the standard piers 40 are attached to the rails and to pressure treated supports. The standard piers may even be eliminated for some applications in the GAD pier foundation system provides the support for the building structure. FIGS. 2A-2C depict exemplary respective foundation systems with standard piers 40, GAD piers 50 for a single wide building structure 10′, a double wide structure 10″ with a tag unit, and a triple wide structure 10′″ with chassis rails 14.

An exemplary embodiment of a GAD pier 50 is illustrated in FIG. 3. The exemplary pier 50 includes a top plate 52 welded to atop end of a tube 54. The bottom end of the tube is welded to a lower plate 56. In an exemplary embodiment, the top plate may be a ⅝ inch thick steel plate, which is 6 inches wide by 10 inches long. The tube 54 may be a 3 inch square structural steel tube, with ¼ inch thick walls. The lower plate 56 may be an 8 inch square, ½ inch thick, steel plate.

The exemplary pier 50 embodiment may also include a bottom plate 58, which in an exemplary embodiment may be a 12 inch square, ½ inch thick, steel plate, with corner holes 58A formed therein for securing the pier to a foundation bolt system.

In an exemplary embodiment, the lower plate 56 may be attached to the bottom plate 58 by a sandwich arrangement of bearings structures 60, 62 and 64, and bars 66, 68. The bearing structures may be fabricated of polyurethane, for example. By way of further example, bearing structures 60, 62 may be 1 inch thick by 2 inch wide by 8 inch long polyurethane blocks, and bearing structure 64 may be a 1 inch thick by 8 inch wide by 8 inch long polyurethane block. The polyurethane in an exemplary embodiment may conform to the following characteristics: free from voids and imperfections; elastic modulus between 200 psi and 1000 psi over a temperature range of −20 degrees F. to +120 degrees F.; modulus of rigidity between 10% to 33% of the elastic modulus over the temperature range; fraction of critical damping over temperature range of interest (e.g., −20 degrees F. to 120 degrees F.) for both axial and shear distortions not less than 30% of critical; tensile strength of 100 psi or greater; Brinell hardness of 10 or greater; not susceptible to significant creep; long term creep strains not exceeding three times normal elastic strains.

In an exemplary embodiment, the polyurethane bearing structures and the lower plate are captured between the bottom plate 58 and rigid plates 60, 62, 66 and 68. In an exemplary embodiment, the rigid plates 60, 62, 66, 68 are ½ inch thick by 2 inch wide by 8 inch long steel plates, with ½ inch diameter bolt holes formed at each end to receive the fastening bolts, as shown in further detail in FIG. 4.

The pier 50 may be attached to a chassis beam 14 of the housing structure 10. In an exemplary embodiment, a pair of wood shims 84, 86 sandwich the beam 14, and in turn are captured between angle structures 80, 82. The angle structures 80, 82 may in an exemplary embodiment be fabricated of ⅜ inch thick steel, and have bolt openings formed therein to receive mounting bolts therethrough to secure the sandwiched assembly of the chassis beam 14, the wood shims 84, 86 and the angle structures 80, 82 together. The angle structures 80, 82 may also have bolt openings formed therein to receive bolts therethrough to secure the angle structures to the top plate 52. For example, the angle structure may have a ¾ inch diameter opening 82A and ½ inch diameter openings 82B formed therein. The top plate 52 has corresponding bolt openings formed therein at each corner to receive the mounting bolts which fasten the top plate to the angle structures and the chassis rail of the structure 10.

FIG. 4 illustrates the lower portion of an exemplary GAD pier 50 in cross-sectional view, as affixed to an exemplary concrete footing 22. The pier 50 is supported above the top surface 22A of the pier 50 by a set of angle bolts 100, one for each corner of the bottom plate 58. Each angle bolt 100 has an angle end portion embedded in the footing 22, e.g. in an exemplary embodiment at least 5 inches below the top surface 22A. The threaded end 100B of each bolt 100 is passed through a bolt opening 58A (FIG. 3) formed in a corner of the bottom plate 58. A pair of threaded nuts 102, 104 secure the plate and bolt, with the lower nut 102 fixing the set-off distance of the plate 58 above the footing surface, and the top nut 104 securing the plate to the bolt against the lower nut. In an exemplary embodiment, the set-off distance does not exceed three inches. In an exemplary embodiment, the angle bolts are ¾ inch diameter bolts. In an exemplary embodiment the angle ends of the bolts 100 may be aligned on a diagonal relative to the bolt pattern defined by the four bolts 100. During construction of the footing, the bolts 100 may be placed in the wet poured concrete by a template, to ensure the bolt pattern will match the hole pattern in the bottom plate 58.

FIG. 4 also illustrates an exemplary arrangement of threaded bolts 92 and nuts 94, which secure the assembly of the bottom plate 58, lower plate 56, plates 66, 68 (66 and 68 depicted in FIG. 3), 70, 72, and bearing structures 60, 62, 64. Annular bushings 90 are assembled around the respective bolts 92. In an exemplary embodiment, the bushings 90 are fabricated of a soft material such as lead. In an exemplary embodiment, the bolts 90 may be ½ inch diameter bolts, and the nuts 94 are torqued on the bolts 92 to 5 foot-pounds or less. The bushings 90 may have a height of 1 inch, an outer diameter of 0.875 inch and an inner diameter of 0.512 inch, in an exemplary embodiment. The bushings may be softer than the polyurethane material of the bearings, and so deform under forces applied, e.g. during a seismic event or due to high winds, before the bearings deform. This may reduce fracturing of the bearings during such earth movement, as well as allow some limited movement of the lower plate 56 relative to the bottom plate 58.

FIGS. 5-6 illustrate an exemplary construction of the footing 22. In an exemplary embodiment, the concrete footing 22 has a thickness of at least 6 inches, and length and width dimensions of at least 2 feet. Anchor rods 110 protrude diagonally from the corners of the footing 22 by a protrusion length of at least 12 inches. In an exemplary embodiment, the rods 110 are at least 20 inches long, and thus are embedded within the footing to a length of 8 inches in this example. The rods 110 in one exemplary embodiment have an outer diameter of ¾ inch, and may be fabricated from reinforced steel or rebar. In one exemplary embodiment, the protruding ends of the anchor rods 110 extend downwardly from the concrete footing at approximately a 45 degree angle. Preferably, the footings and anchor rods provide an effective footing weight or uplift capacity of at least 10,000 pounds in one exemplary embodiment. The top surface 22A of the footing is positioned above the natural grade 24 by a distance of 2 inches or so, in one exemplary embodiment.

The footings 22 may be constructed on site. Alternatively, the footings 22 may be prefabricated, and then installed on the building site. For construction on site, the footing hole may be dug into the ground at the appropriate permanent location of the footing. Forms may be used to define the footing in some applications. For other sites, the hole is dug to the appropriate size and the hole walls define the footing size. The rods 110 may be augered into the ground to an appropriate depth, with ends exposed in the hole. Wet concrete may be poured into the hole, embedding the exposed ends of the rods in the wet concrete. The angled ends of the angle bolts 100 may be inserted into the wet concrete to the appropriate depth, using a template to position the bolts so that the spacing is correct to match the opening configuration in the bottom plate of the GAD pier 50.

In operation, the GAD piers 50 may function to allow some limited movement of the chassis rail 14 relative to the concrete footing 22, due to the bearings and bushings which will deflect or deform in response to shaking or movement of the earth due to earth tremors or earthquakes, or due to forces applied during high winds, while still maintaining a connection between the rail and footing. Thus, the GAD piers 50 may help to mitigate the effects of tremblers and high winds by providing some measure of flexible support to a securely anchored structure.

Although the foregoing has been a description and illustration of specific embodiments of the invention, various modifications and changes thereto can be made by persons skilled in the art without departing from the scope and spirit of the invention as defined by the following claims. 

1. A pier for a foundation system for a manufactured building structure, comprising: a top plate structure adapted for attachment to the manufactured building structure; a lower plate structure; a generally vertical rigid member attached between the top plate structure and the lower plate structure; a bottom plate structure attached to a foundation footing; a bearing structure for connecting the lower plate structure to the bottom plate structure and adapted to allow limited movement between the bottom plate structure and the lower plate structure in response to forces applied during seismic events and high winds.
 2. The pier of claim 1, wherein said manufactured building structure includes a chassis rail, the pier further comprising a bracket structure for attaching the top plate structure to the chassis rail.
 3. The pier of claim 1, wherein said bearing structure comprises a plurality of polyurethane bearing structures sandwiching the lower plate structure.
 4. The pier of claim 3, wherein said plurality of polyurethane bearing structures includes a lower generally planar polyurethane structure for mounting against a bottom facing surface of the lower plate structure, and a pair of upper generally planar polyurethane structures for mounting against a top surface of the lower plate structure.
 5. The pier of claim 4, wherein said bearing structure further comprises a pair of rigid plate members positioned on respective top surfaces of the pair of upper polyurethane structures, and a plurality of threaded bolt and nut pairs for securing the bearing assembly together and to the lower plate structure and the bottom plate structure.
 6. The pier of claim 5, wherein the plurality of threaded bolts are passed through openings formed in said polyurethane structures.
 7. The pier of claim 6, further comprising a plurality of annular bushings positioned between the threaded bolts and said polyurethane structures, said bushings fabricated of a softer material than said bearings.
 8. The pier of claim 7, wherein said annular bushings are fabricated of lead.
 9. The pier of claim 1, wherein the foundation footing comprises a concrete footing, the pier further including a set of threaded angle bolts each having an angle end portion embedded in the concrete footing and an exposed threaded end for securing the bottom plate to the concrete footing.
 10. The pier of claim 1, wherein the generally vertical rigid member is fabricated of a hollow tube member.
 11. The pier of claim 9, wherein the foundation footing further comprising a plurality of anchor rods protruding outwardly from the concrete footing and embedded in soil.
 12. A foundation system for a manufactured building structure, comprising: a plurality of support piers positioned between a site ground surface and said building structure; a plurality of permanent foundation piers, each pier comprising: a top plate structure adapted for attachment to the manufactured building structure; a lower plate structure; a generally vertical rigid member attached between the top plate structure and the lower plate structure; a bottom plate structure attached to a foundation footing; a bearing structure for connecting the lower plate structure to the bottom plate structure and adapted to allow limited movement between the bottom plate structure and the lower plate structure in response to forces applied during siesmic events and high winds.
 13. The system of claim 12, wherein said manufactured building structure includes a chassis rail, the pier further comprising, for each of said plurality of permanent foundation piers, a bracket structure for attaching the top plate structure to the chassis rail.
 14. The system of claim 12, wherein said bearing structure comprises a plurality of rigid bearing structures sandwiching the lower plate structure.
 15. The system of claim 14, wherein said plurality of rigid bearing structures includes a lower generally planar rigid bearing structure for mounting against a bottom facing surface of the lower plate structure, and a pair of upper generally planar rigid bearing structures for mounting against a top surface of the lower plate structure.
 16. The system of claim 15, wherein said bearing structure further comprises a pair of rigid plate members positioned on respective top surfaces of the pair of upper polyurethane structures, and a plurality of threaded bolt and nut pairs for securing the bearing assembly together and to the lower plate structure and the bottom plate structure.
 17. The system of claim 16, wherein the plurality of threaded bolts are passed through openings formed in said rigid bearing structures.
 18. The system of claim 17, further comprising a plurality of annular bushings positioned between the threaded bolts and said rigid bearing structures, said bushings fabricated of a softer material than said rigid bearing structures.
 19. The system of claim 18, wherein said annular bushings are fabricated of lead.
 20. The system of claim 18 wherein said rigid bearing structures are fabricated of polyurethane.
 21. The system of claim 12, wherein the foundation footing comprises a concrete footing, the pier further including a set of threaded bolts each having an exposed threaded end for securing the bottom plate to the concrete footing.
 22. The system of claim 21, wherein the foundation footing further comprising a plurality of anchor rods protruding outwardly from the concrete footing and embedded in site soil. 